1. Field of the Invention
The present invention relates to a method of manufacturing carbon substrates for magnetic disks for data storage including a texture treatment process of roughening the surfaces of the carbon substrates, and particularly to a texture treatment process for carbon substrates which is applicable to manufacturing magnetic disks with low static friction or stiction to the magnetic heads.
2. Description of the Related Art
Recently, with an increase in the amount of information to be recorded, there have been strong demands on magnetic disks as external recorders with large storage capacity and high recording density.
For improvement of the recording density from the viewpoint of the magnetic head, the decrease in the flying height of the magnetic head is effective to obtain high density. However, to reduce the flying height of the magnetic head, the substrate is required to meet severe requirements in flatness and surface roughness. At the present time, flying height of 0.3 .mu.m or less is necessary for achieving high density recording. In this case, the surface roughness required for the substrate is one-tenth or less of the flying height.
However, for the surfaces of the commonly used aluminum alloy substrates themselves, it is impossible to obtain such a low surface roughness. NiP/Al substrates have been used for the t in-film media wherein the surfaces of the aluminum alloy substrates are plated with electroless NiP films for hardening the surfaces and reducing the defects. Surface roughness can be reduced by using this NiP/Al substrate.
On the other hand, if the surface roughness is excessively reduced, there occurs a problem that the magnetic head is attracted to the magnetic disk surface. This attraction phenomenon is based on the following cause: namely, when the slider surface of the magnetic head and the magnetic disk surface, which are finished to be extremely smooth, are opposed to each other with a micro-gap, the gap is buried by the molecules of O.sub.2, N.sub.2, H.sub.2 O and the like, to thereby generate a large attracting force due to the viscous forces and Vander Waals forces. The above attracting force causes the consumption of a large electric power at the starting of the motor, and further, in the worst case, causes damage to the magnetic head or magnetic disk. As a method of preventing such an attraction phenomenon, for the purpose of reducing the contact area between the slider surface of the magnetic head and the magnetic disk surface, there has been commonly adopted a texture treatment process of controlled roughening of the surface of the substrate. However, the roughening of the surface of the NiP/Al substrate by machining i difficult because of generation of the burrs peculiar to metal. Accordingly, achievement of low flying height of the magnetic head using the NiP/Al substrate i difficult. Further, for improvement of the magnetic characteristic, deposition at higher substrate temperature is preferable, but there occurs a problem due to the magnetization generated by the crystallization of the amorphous NiP at high temperatures.
Various substrates in place of the NiP/Al substrate have been proposed. One arrangement relates to use of a carbon substrate for the magnetic disk, which has the features of high heat resistance, non-magnetic property, lightweight and the like (Sato, and others; Abstract of 37th Associated Meeting of Japan Society of Applied Physics, No. 29a-Y-8, 1990).
In a known texture treatment process of the carbon substrate for the magnetic disk, a carbon substrate after surface polishing is heated at 400.degree.-700.degree. C. in an oxidizing atmosphere (Japanese Patent Laid-open No. hei 3-283018).
The above problems can be all solved by using the carbon substrate subjected to uniform surface roughening. Namely, by surface roughening of the carbon substrate, the attraction between the magnetic disk surface and the magnetic head is reduced and the generation of burrs observed in the NiP/Al substrate is eliminated, which enables the low flying height performance of the magnetic head. Further, since the carbon substrate has a high heat resistance, it is possible to improve the medium performance, and hence to manufacture the magnetic disk with high recording density.
However, the conventional roughening method of heating the carbon substrate after surface polishing a 400.degree.-700.degree. C. in an oxidizing atmosphere is disadvantageous since it increases the manufacturing cost because of its longer treatment time. Also, since the temperature control is difficult, the surface roughness is locally varied in each substrate, thereby generating a variation of the surface roughness in the surface of each substrate, and generating a variation of the surface roughness among the substrates in each lot.